PROJECT SUMMARY Fetal transitioning from the relatively hypoxic in utero environment to an oxygen-rich perinatal atmosphere represents an oxidative burden on the developing lung. Preterm lungs are already deficient in antioxidants and are poorly equipped to deal with this oxidative transition following parturition even before considering the adverse effects of therapeutic oxygen and ventilation required to treat poor respiratory function. Sustained therapeutic oxygen may result in bronchopulmonary dysplasia (BPD), a significant morbidity and mortality in preterm infants marked by alveolar simplification and dysmorphic vascular growth. It is imperative to identify and define how oxygen-sensitive signaling pathways contribute to alveolar growth and injury in settings of altered oxygen tension. Reversible oxidation of cysteine thiols has emerged as an important signaling paradigm to modulate protein activity in response to redox perturbations. Such thiol switches are regulated by the enzyme activities of thioredoxin and glutathione superfamilies. We recently identified thioredoxin-1 (Trx1) and thioredoxin-2 (Trx2) as critical regulators of cysteine oxidation during hyperoxic injury. We hypothesize that Trx1 and Trx2 act as molecular sensors of atmospheric oxygen tension that modulate alveolar development and injury/repair responses during redox perturbations associated with developmental oxidative transitions during parturition and hyperoxic injury. However, the physiological contribution of redox signaling via thioredoxin-dependent thiol switches is unknown since genetic disruption of either Trx1 or Trx2 expression is embryonic lethal and in vivo data are exclusively generated with overexpression of transgenes. The following Aims investigate how thioredoxin regulation thiol switches influences tissue and cellular physiologies and molecular functions in response to redox perturbations caused by atmospheric oxygen tension Determine if : (1) Trx1 activity influences alveolar growth and injury during oxygen transitions, (2) Identify oxygen-sensitive Trx1- dependent signaling pathways regulated via reversible oxidation of cysteine thiols, and (3) Examine how Trx2 regulates oxygen-induced mitochondrial injury and lung epithelial cell death. Fundamental knowledge gained from this project will provide new understanding on thioredoxin-dependent thiol switches regulation of responses during redox perturbations. The overarching goal of this project is to accelerate the discovery of key thioredoxin regulatory nodes of redox-dependent signaling networks and harness this information for the development of new diagnostic and therapeutic approaches for BPD. alveolar development and injury